Substrate for manufacturing a semiconductor device with three element alloy

ABSTRACT

The substrate according to the present invention is comprised of a silver/gold/grain element alloy layer, wherein the alloy forms an outside layer of the product. The grain element is selected from a group consisting of selenium, antimony, bismuth, nickel, cobalt, indium and combination thereof. The present invention has a particular application in forming the outside layer of various items, including a lead frame, a ball grid array, a header, a printed circuit board, a reed switch and a connector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate comprising a three element alloy, and particularly, relates to a substrate wherein the three element alloy comprising the Au/Ag/grain element is applied to a nickel layer which is applied to the copper or copper alloy, or nickel or nickel alloy, to provide the desired characteristics of improved bondability, corrosion durability, adhesion to mold resin and cost effectiveness.

2. Background Art

Generally, the substrates for a semiconductor device make electrical interconnections between electrical and electronic devices, which includes such devices as a semiconductor chip and a printed circuit board (“PCB”). Moreover, the characteristics of a good substrate material include bondability to connecting wires, durability from corrosion, adhesion to the mold resin (which typically acts as a cover), and ductility for manipulation.

To achieve such characteristics, conventional substrates for a semiconductor device have used an outermost layer of Sn—Pb in a multi-plated layer structure also including a copper layer and nickel layer, However, lead is widely considered to be a health hazard. Lead is toxic to human individuals and it has a long documented history of adverse impact on humans and the environment.

Conventionally, alternatives to the Sn—Pb layer have been a palladium layer or a gold layer as the outermost layer. However, a palladium layer or a gold layer has manifest problems in wire bondability, adhesion to the mold resin, and attachment characteristics for a PCB. Additionally, the costs of using palladium and of gold have traditionally been fairly high.

SUMMARY OF THE INVENTION

An object of the present invention is to provide substrates that are lead-free and thus environmentally friendly, while at the same time, providing the desired characteristics of improved bondability, corrosion durability, adhesion to mold resin, and cost effectiveness.

To achieve this object, the present invention uses the three element alloy comprising gold, silver and grain element selected from selenium, antimony, bismuth, nickel, cobalt and indium.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned aspects and other features of the invention will be explained in the following description, taken in conjunction with the accompanying drawing therein

The accompanying drawing is a diagram of the substrate to which the three element alloy layer is applied, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The substrate of the present invention comprises a patterned copper layer, a nickel layer having a thickness of 10-300 microinches, deposited on said patterned copper layer, and a three element alloy layer consisting of gold/silver/grain element and having a thickness of 3-160 microinches, deposited on said nickel layer.

The three element alloy layer comprises 50-95wt % of silver, 4-49wt % of gold and 1% or less of one of the grain elements. The grain element is selected from the group consisting of selenium, antimony, bismuth, nickel, cobalt and indium and more preferably, selenium. The addition of the grain element aids in refining grain morphology and decreasing the porosity of a deposited metal.

For the present invention, the nickel layer prevents the diffusion of the copper and improves the solder wettability upon mounting the package of the semiconductor chip onto the printed circuit board. The thickness of the nickel layer preferably ranges from 10 to 300 microinches. The upper, three elements alloy layer prevents the diffusion of the metals in the lower layers by heat, prevents the upper layer from oxidation and increases bondability with gold wire during wire bonding with the silicon chip. The thickness of the three element alloy layer preferably ranges from 3 to 160 microinches.

The substrate of the present invention has the characteristic that electric or electronic devices can be mounted without the plating of the Pb/Sn alloy. Further, as reported previously, silver has the problem that the adhesion to mold resin is decreased due to hygroscopicity but due to the present invention, such a problem is avoided.

The present invention can be used in manufacturing a lead frame, a ball grid array, a header, a printed circuit board, a Reed switch, a connector and various electronic components.

EXAMPLE

The present invention has been tested as detailed below. The test was conducted using gold/silver/selenium alloy, which is the most preferred alloy.

The Preparation of the Sample

The surface of the copper or copper alloy coil was degreased and activated by acid. The Ni and Au/Ag/selenium alloy was the electroplated orderly onto the entire surface of the copper or copper alloy base material.

Test for Evaluation of Bondability

After wire binding was conducted using a wire-bonding machine, the tensile strength was measured by using a bonding pull tester.

Test for Evaluation of Solder Wettability

After heat treatment at 175 for 7 hours and half, the sample was aged forcibly at 95 under 95% relative humidity for 8 hours. And, then evaluation of solder wettability was conducted, referring to MIL-STD-883D.

Test for Evaluation of Adhesion to Mold Resin

After the sample was sealed with a mold resin at molding temperature of 170 for 90 seconds and treated for 6 hours at 175 by heat, the adhesion between the substrate of the semiconductor device and mold resin was evaluated by using a SAT (Scanning Acoustic Tomograph) referring to the MRT (Moisture Resistance Test). The range of temperature was 55 to 125, and before to SAT was performed, the sample was cured at 125 for 24 hours.

Example 1 and Comparative Example 1

Evaluation Test on Bondability

The results of each of the evaluation tests are shown in Tables 1 and 2. In the Tables, the conditions prepared for each example are marked as symbol “•”. Table 1 represents the results of the evaluation test for the layer plated according to the present invention and Table 2 represents the results of the evaluation test for the layer on which Au or Ag alone, or Au/Ag alloy is deposited, for comparison. In Table 2, samples 12-18 are for Ag alone, samples 19-24 are for Au alone and samples 25-30 are for Au/Ag alloy.

TABLE 1 Laminate Tensile Structure Strength Thickness Ni Au/Ag/Se EDS Analysis in Wire (μin) 30 50 70 5 10 15 (wt %) Bonding (g) Sample 1    Au 11, Ag 89 15.30 Sample 2    Au 16, Ag 84 15.60 Sample 3    Au 22, Ag 78 15.40 Sample 4    Au 27, Ag 73 15.40 Sample 5    Au 30, Ag 70 15.36 Sample 6    Au 35, Ag 65 16.21 Sample 7    Au 30, Ag 70 15.21 Sample 8    Au 33, Ag 67 16.21 Sample 9    Au 32, Ag 68 16.71 Sample 10   Au 34, Ag 66 16.15 Sample 11   Au 31, Ag 69 14.87 Sample 12   Au 31, Ag 69 15.88

TABLE 2 Laminate Tensile Structure Ag, Au or Strength Thickness Ni Au/Ag EDS Analysis in Wire (μin) 30 50 70 5 10 15 (wt %) Bonding (g) Sample 13   Ag 100 — Sample 14   Ag 100 — Sample 15   Ag 100 — Sample 16   Ag 100 — Sample 17   Ag 100 — Sample 18   Ag 100 — Sample 19   Au 100 11.25 Sample 20   Au 100 12.31 Sample 21   Au 100 12.33 Sample 22   Au 100 11.26 Sample 23   Au 100 10.55 Sample 24   Au 100 10.99 Sample 25   Au 11, Ag 89  9.66 Sample 26   Au 16, Ag 84  9.55 Sample 27   Au 22, Ag 78 10.25 Sample 28   Au 27, Ag 73 10.22 Sample 29   Au 30, Ag 70 11.23 Sample 30   Au 35, Ag 65 10.56

From the results of Tables 1 and 2, it is clear that the samples having a layer of Au/Ag/Se alloy show higher values in the tensile strength of wire bonding than samples having a layer of Au or Ag alone, or Au/Ag alloy. Also, as only Ag existed as an outermost layer, a gold wire could not be bonded on the surface of the Ag layer. Although a gold wire could be bonded on the surface of the Au/Ag alloy, the layer of Au/Ag/Se alloy according to the present invention showed much higher value in the tensile strength of the wire bonding than that of the Au/Ag alloy. In Table 1, the Se content was not detected by Energy Disperse Spectroscopy (EDS) analysis since only a small amount of Se was contained.

Example 2 and Comparative Example 2

Evaluation on Solder Wettability

The samples were evaluated on solder wettability. The condition of the samples was the same as Example 1 and Comparative Example 1. The results of the evaluation of the samples according to the present invention are presented in Table 3, and the results for the other samples are presented in Table 4. The Se content could not be detected by EDS analysis as in Table 1.

TABLE 3 Laminate Structure Covered Thickness Ni Au/Ag/Se EDS Analysis Amount (μin) 30 50 70 5 10 15 (wt %) (%) Sample 1    Au 11, Ag 89 99-100 Sample 2     Au 16, Ag 84 99-100 Sample 3    Au 22, Ag 78 99-100 Sample 4    Au 27, Ag 73 99-100 Sample 5    Au 30, Ag 70 99-100 Sample 6    Au 35, Ag 65 99-100 Sample 7    Au 30, Ag 70 99-100 Sample 8    Au 33, Ag 67 99-100 Sample 9    Au 32, Ag 68 99-100 Sample 10   Au 34, Ag 66 99-100 Sample 11   Au 31, Ag 69 99-100 Sample 12   Au 31, Ag 69 99-100

TABLE 4 Laminate Structure Ag, Au or Covered Thickness Ni Au/Ag EDS Analysis Amount (μin) 30 50 70 5 10 15 (wt %) (%) Sample 13   Cu3, Ni5, Ag92 58 Sample 14   Cu2, Ni4, Ag94 65 Sample 15   Cu1, Ni4, Ag95 70 Sample 16   Cu4, Ni3, Ag93 55 Sample 17   Cu2, Ni4, Ag94 65 Sample 18   Cu1, Ni4, Ag95 75 Sample 19   Cu2, Ni5, Ag93 72 Sample 20   Cu1, Ni4, Ag95 80 Sample 21   Cu1, Ni3, Ag96 89 Sample 22   Cu4, Ni3, Ag93 77 Sample 23   Cu1, Ni1, Ag98 80 Sample 24   Cu1, Ni1, Ag98 90 Sample 25   Ni5, Au11, Ag84 94 Sample 26   Ni4, Au16, Ag80 95 Sample 27   Ni2, Au22, Ag76 95 Sample 28   Ni3, Au27, Ag70 94 Sample 29   Ni4, Au30, Ag66 96 Sample 30   Ni4, Au35, Ag61 94

According to the results of Table 4, Ni and Cu were detected by EDS analysis on the surface of Au or Ag alone, or Au/Ag alloy in samples 13 to 24. Also, the covered amount (%) of solder in an evaluation on solder wettability did not reach above the 95%, pass limit. As a result, the diffusion of Ni or Cu made the substrates deteriorate in solder wettability. On the other hand, according to the 20 results of Table 3, the samples having an outermost layer of Au/Ag/Se alloy which were not contaminated by the diffusion of Ni or Cu all passed in an evaluation on solder wettability, showing a reading of over 99%.

Example 3 and Comparative Example 3

Evaluation on Adhesion of Mold Resin

The samples were evaluated on adhesion of the mold resin. The condition of the samples was the same as in Example 1 and comparative Example 1. The results of the evaluation for the samples according to the present invention are presented in Table 5, and the results for other samples are presented in Table 6. In comparative example 3, the layer of Au/Ag alloy was not used.

TABLE 5 Laminate Structure Thickness Ni Au/Ag/Se EDS Analysis Adhesion of (μin) 30 50 70 5 10 15 (wt %) Mold Resin Sample 1    Au 11, Ag 89 Pass Sample 2    Au 16, Ag 84 Pass Sample 3    Au 22, Ag 78 Pass Sample 4    Au 27, Ag 73 Pass Sample 5    Au 30, Ag 70 Pass Sample 6    Au 35, Ag 65 Pass Sample 7    Au 30, Ag 70 Pass Sample 8    Au 33, Ag 67 Pass Sample 9    Au 32, Ag 68 Pass Sample 10   Au 34, Ag 66 Pass Sample 11   Au 31, Ag 69 Pass Sample 12   Au 31, Ag 69 Pass

TABLE 6 Laminate Structure Adhesion of Thickness Ni Ag or Au EDS Analysis Mold Resin (μin) 30 50 70 5 10 15 (wt %) (%) Sample 13   Ag 100 Failure Sample 14   Ag 100 Failure Sample 15   Ag 100 Failure Sample 16   Ag 100 Failure Sample 17   Ag 100 Failure Sample 18   Ag 100 Failure Sample 19   Au 100 Pass Sample 20   Au 100 Pass Sample 21   Au 100 Pass Sample 22   Au 100 Pass Sample 23   Au 100 Pass Sample 24   Au 100 Pass

According to the results of Tables 5 and 6, the sample of Au or Au/Ag/Se alloy deposited as an outermost layer on the Ni plated layer attain better adhesion of mold resin than the sample of only Ag deposited as an outermost layer on the Nickel plated layer. If the SAT system detected voids or gaps between the substrates and mold resin, the sample was considered as a failure.

It is understood that while the various particular embodiments set forth herein have been described in detail, the description has been given for illustrative purposes only, and it is to be understood that changes and variables may be made without departing from the spirit or scope of the following claims. 

What is claimed is:
 1. A substrate for semiconductor device comprising: a patterned copper layer; a nickel layer having a thickness of 10-300 microinches, deposited on said patterned copper layer; and a three element alloy layer consisting of gold/silver/grain element and having a thickness of 3-160 microinches, deposited on said nickel layer.
 2. A substrate according to claim 1, wherein the said grain element is selected from a group consisting of Se, At, Bi, Ni, Co and In.
 3. A substrate according to claim 1, wherein said three element alloy contains 50-95 wt % of Ag, 4-49 wt % of Au and less than 1 wt % of grain element.
 4. A substrate according to claim 1 for use in manufacturing electronic components, a printed circuit board, a ball grid array and a lead frame. 